1. Field of the Invention
The present invention relates to an image processing apparatus and a method for controlling the image processing apparatus, and more specifically relates to technology for measuring an amount of toner adhesion for a toner image that has been formed on an image carrier.
2. Description of the Related Art
The color of an image formed by an electrophotographic image processing apparatus varies due to a change in various physical parameters, even if the settings of the apparatus when forming an image are fixed. In particular, developing and transfer processes contribute in a high proportion to such color variation. When the position of a latent image, amount of toner supplied, transfer efficiency, and so forth change due to environmental variations in temperature, humidity, and so forth, the amount of adhesion of toner that adheres to a photosensitive drum or a transfer belt is not stable. Therefore, it is necessary to stabilize the developing and transfer processes by measuring the amount of toner adhesion on the photosensitive drum or on the transfer belt, and performing feedback control of an exposure amount, developing voltage, transfer current, and so forth based on the results of that measurement.
Ordinarily, such control is performed when variation in the printer environment occurs, such as after exchanging toner cartridges, after printing a predetermined number of pages, or after turning on power to the main body of the printer. When measuring the amount of toner adhesion, the image processing apparatus forms a plurality of toner patches of various densities from low density to high density on the photosensitive drum or on the transfer belt. Furthermore, the amount of toner adhesion of these toner patches is measured with a toner adhesion amount measuring apparatus, and various controls are performed with appropriate image forming conditions based on the results of that measurement.
Here, technology for measuring the amount of toner adhesion is disclosed in Japanese Patent Laid-Open Nos. 62-280869, 3-209281, and 8-327331. Japanese Patent Laid-Open Nos. 62-280869 and 3-209281 disclose a method in which the amount of reflected light when light is irradiated on an image carrier, and the amount of reflected light when light is irradiated on a toner patch, are detected, the amount of toner adhesion is measured from the change in these amounts of reflected light, and image density parameters are controlled based on this measured value.
Also, Japanese Patent Laid-Open No. 8-327331 discloses a method for detecting the amount of toner adhesion by measuring the thickness of a toner patch with a laser displacement gauge. In this method, spot light is irradiated on an image carrier to form an image of reflected light at a position corresponding to the thickness of a toner patch that adheres onto the image carrier, and the amount of toner adhesion is measured by detecting a change in the position of the formed image with a PSD (Position Sensing Device). Afterward, feedback control of image density parameters of the capture system is performed based on the results of that measurement.
However, in the schemes for measuring the amount of toner adhesion based on the amount of reflected light that are described in Japanese Patent Laid-Open Nos. 62-280869 and 3-209281, there is the problem that the accuracy of measurement worsens in an area with higher density.
In the case of measuring the amount of toner adhesion from the reflection position described in Japanese Patent Laid-Open No. 8-327331, the physical shape of the toner patch is measured, so it is possible to measure the amount of adhesion regardless of the toner color. However, with this scheme, there is the problem that the accuracy of measurement worsens in an area with lower density.